UV-cured multi-component polymer blend electrolyte, lithium secondary battery and their fabrication method

ABSTRACT

The present invention relates to a UV-cured multi-component polymer blend electrolyte, lithium secondary battery and their fabrication method, wherein the UV-cured multi-component polymer blend electrolyte, comprises: A) function-I polymer obtained by curing ethyleneglycoldi-(meth)acrylate oligomer of formula 1 by UV irradiation, CH 2 ═CR 1 COO(CH 2 CH 2 O) n COCR 2 ═CH 2  (1) wherein, R 1  and R 2  are independently a hydrogen or methyl group, and n is an integer of 3-20; B) function-II polymer selected from the group consisting of PAN-based polymer, PMMA-based polymer and mixtures thereof; C) function-III polymer selected from the group consisting of PVdF-based polymer, PVC-based polymer and mixtures thereof; and D) organic electrolyte solution in which lithium salt is dissolved in a solvent.

TECHNICAL FIELD

The present invention relates to a multi-component polymer blendelectrolyte cured by ultraviolet (hereinafter referred to as “UV”) raysand a lithium secondary battery and a fabrication method thereof. Moreparticularly, the UV-cured multi-component polymer electrolyte comprisesthe following components:

A) a function-I polymer obtained by curing anethyleneglycoldi(metha)acrylate oligomer having the following formula 1by UV irradiation,CH₂═CR¹COO(CH₂CH₂O)_(n)COCR²═CH₂  (1)

wherein, R¹ and R² are independently a hydrogen or methyl, and n isinteger of 3–20;

B) a function-II polymer selected from the group consisting ofpolyacrylonitrile (PAN), polymethylmethacrylate (PMMA) and mixturesthereof;

C) a function-III polymer selected from the group consisting ofpolyvinylidene fluoride (PVdF), polyvinyl chloride (PVC) and mixturesthereof; and

D) an organic electrolyte solution in which a lithium salt is dissolvedin an organic solvent.

BACKGROUND ART

Since it was reported the fact that a complex of polyethylene oxide(PEO) or polypropylene oxide (PPO) with a lithium salt showed an ionicconductivity in a solid state at ambient temperature, researches forutilizing it have been actively performed. However, according to thereport of Armand et al., a polymer electrolyte using the PEO as a matrixexhibits a low ionic conductivity of below 10⁻⁸ S/cm due to its hightendency to crystallize at ambient temperature, and accordingly it couldnot be utilized. Recently, a polymer electrolyte of gel type which isplasticized after adding an organic electrolyte solution into a polymermatrix such as PMMA, PAN or PVC has been developed by G. Freuillade, M.Watanabe, E. Ysushida and Q. Wixwat et at. In the above plasticizedpolymer electrolyte in gel form, a lithium salt dissolved in an organicsolvent presents in the polymer matrix having a dipole moment. Inaddition it exhibits an ionic conductivity of no less than 10⁻³ S/cmunder a condition that the ratio of organic solvent and the lithium saltis optimized, and therefore, it has been highlighted as a polymerelectrolyte system having a highest possibility to be utilized. However,in order to fabricate the above polymer electrolyte in gel type, adrying process should be performed after a heating process at over 100°C. is performed. In addition, because the matrix exhibits high viscosityin a melted state, the practical assembling process becomes complex, andthe fabrication cost is increased.

U.S. Pat. No. 4,830,939 discloses a method for preparing a UV-curedpolymer electrolyte by mixing a polyethylene composition having at leastone unsaturated functional groups with a liquid electrolyte and thenplasticizing the resultant with a cross-linking polymerization using aUV curing method. Although the UV-cured polymer electrolyte prepared bythe above method exhibits a high ionic conductivity, the oligomer usedas a matrix has a low mean molecular weight of 300–400, and therefore,it has a disadvantage in that its flexibility is relatively low.

In addition, European Patent No. 0 638 950 A1 discloses a method forpreparing a UV cured polymer electrolyte which is plasticized with across-linking polymerization of a composition in which poly(ethyleneglycol)-diacrylate (PEGDA) and a liquid electrolyte are mixed. The meanmolecular weight of the oligimer used in this method, that is PEGDA, islimited to be no more than 440. However, the UV-cured polymerelectrolyte prepared by the above method is a glassy polymer which has ahigh brittleness and therefore can not be stretched, to result a failureof its utilization.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a UV-curedpolymer blend electrolyte which is superior in adhesive property to anelectrode, compatibility with an organic electrolyte solution for alithium secondary battery, ionic conductivity and mechanical strength,and has an improved processability in fabrication of a battery, and toprovide a preparation method thereof.

Another object of the present invention is to provide a lithiumsecondary battery comprising the above UV-cured polymer blendelectrolyte.

To achieve the above object of the present invention, there is provideda UV-cured polymer electrolyte which is obtained by curing with UV raysa combination of a UV-curable oligomer, a polymer which is superior inadhesive property to an electrode and ionic conductivity, and a polymerwhich is superior in compatibility with an organic solvent electrolyte.

In more detail, the above object of the present invention is achieved byproviding a UV-cured polymer blend comprising the following components:

A) a function-I polymer obtained by curing anethyleneglycoldi(metha)acrylate oligomer having the following formula 1by UV irradiation,CH₂═CR¹COO(CH₂CH₂O)_(n)COCR²═CH₂  (1)

wherein, R¹ and R² are independently a hydrogen or methyl, and n is andinteger of 3–20;

B) a function-II polymer selected from the group, consisting ofpolyacrylonitrile (PAN), polymethylmethacrylate (PMMA) and mixturesthereof;

C) a function-III polymer selected from the group consisting ofpolyvinylidene fluoride (PVdF), polyvinyl chloride (PVC) and mixturesthereof; and

D) an organic electrolyte solution in which a lithium salt is dissolvedin and organic solvent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the results of measuring ionic conductivitiesof the UV-cured multi-component polymer blends obtained in Examples 1–4and that of the polymer electrolyte obtained in Comparative Example 1.

FIG. 2 is a graph showing the testing results of electrode capacitiesand cycle life of lithium secondary batteries obtained in Examples 1–9and in Comparative Examples 1 and 2.

FIG. 3 a is a graph showing the test results of low and high temperaturecharacteristics of the lithium secondary battery of the presentinvention obtained in Example 1, and FIG. 3 b is a graph showing thetest results of low and high temperature characteristics of the lithiumsecondary battery obtained in Comparative Example 1.

FIG. 4 a is a graph showing the test results of a high-rate dischargecharacteristics of the lithium secondary battery of the presentinvention obtained in Example 1; and FIG. 4 b is a graph showing thetest results of a high-rate discharge characteristics of the lithiumsecondary battery obtained in Comparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in detail with reference toaccompanying drawings.

The present invention relates to a UV-cured multi-component polymerblend, a lithium secondary battery and fabrication method thereof. TheUV-cured multi-component polymer electrolyte comprises the followingcomponents:

A) a function-I polymer obtained by curing anethyleneglycoldi-(metha)acrylate oligomer having the following formula1, by UV irradiation,CH₂═CR¹COO(CH₂CH₂O)_(n)COCR²═CH₂  (1)

wherein, R¹ and R² are independently a hydrogen or methyl, and n is aninteger of 3–20;

B) a function-II polymer selected from the group consisting ofpolyacrylonitrile (PAN), polymethylmethacrylate (PMMA) and mixturesthereof;

C) a function-III polymer selected from the group consisting ofpolyvinylidene fluoride (PVdF), polyvinyl chloride (PVC) and mixturesthereof; and

D) an organic electrolyte solution in which a lithium salt is dissolvedin an organic solvent.

In the electrolyte of the present invention, the function-II polymerselected from the group consisting of PAN, PMMA and mixtures thereof andthe function-III polymer selected from the group consisting of PVdF, PVCand mixtures thereof are added to the function-I polymer containingvarious lengths of ethylene oxide group, and thereby the liquidelectrolyte can be easily contained in a polymer matrix. In addition,the entanglement of the polymer chains obtained by polymerizing theoligomer represented by the formula 1 with the function-II and IIIpolymers makes the brittleness which is the disadvantage of theconventional UV-cured polymer electrolyte be reduced, and also improverubber-like property and other properties of the electrolyte.

Although the electrolyte of the present invention actually has asemi-interpenetrating polymer network, herein, it is called as a “blend”for convenience sake.

The oligomer having the formula 1 includes ethleneglycoldiacrylate (R¹and R² are hydrogen), ethyleneglycoldimethacrylate (R¹ and R² aremethyl) or mixtures thereof having a molecular weight of 200–2000. Theamount of the oligomer used can be adjusted in the range of 5–95% of theentire polymer mixture according to the characteristics required. Theoligomer is liquid at the temperature for fabricating the electrolyteand therefore superior in fluidity. In addition, it is polymerized withUV rays, and therefore, the fabricating process can be controlled by theUV radiating condition.

The polymers of PAN and PMMA group used in the present invention canimpregnate a lot of electrolyte and are superior in adhesive propertiesand compatibility with the organic electrolyte solution for lithiumsecondary batteries. The polymers of PVdF and PVC group have rubber-likeproperties and are also superior in mechanical strength and ionicconductivity.

It is preferred that the polymer of PAN group is selected from the groupconsisting of polyacrylonitrile and poly(acrylonitrile-methylacrylate),and the polymer of PMMA group is selected from the group consisting ofpolymethylmethacrylate, poly(methylmethacrylate-co-ethylacrylate) andpoly-(methylmethacrylate-co-methacrylic acid). In addition, It ispreferred that the polymer of the PVdF group is selected from the groupconsisting of polyvinylidene difluoride andpoly(vinylidenedifluoride-hexafluoroprophylene), and, the polymer of PVCgroup is selected from the group consisting of polyvinylchloride andpoly(vinylchloride-co-acrylonitrile).

The lithium salt included in the organic electrolyte solution of thepresent invention is the lithium salt which is generally used forlithium secondary batteries. Examples may include LiPF₆, LiClO₄, LiAsF₆,LiBF₄, LiCF₃SO₃, Li(CF₃SO₂)₂N, etc., and LiPF₆ or LiClO₄ is morepreferable.

Examples of the organic solvent used in the organic electrolyte solutionmay include ethylene carbonate (EC), propylene carbonate (PC), diethylcarbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC)or mixtures thereof. In order to improve low temperature characteristicsof batteries, methyl acetate (MA), methyl propionate (MP), ethyl acetate(EA), ethyl propionate (EP), butylene carbonate (BC), γ-butyrolactone(γ-BL), 1,2-dimethoxyethane (DME), dimethyl acetamide (DMA),tetrahydrofuran or mixtures thereof can further be added to the aboveorganic solvent. The amount of the organic electrolyte solution used ispreferable to be adjusted in the range of 100–2000% by weight of theentire polymer mixture.

The electrolyte of the present invention may further include aninitiator for UV curing, a curing accelerator, a plasticizer, a porousfiller and the like optionally.

The initiator for UV curing which can be used in the present inventionmay not be limited if it is capable of generating a radical by UV raysradiated. Examples of such initiator may include2,2-dimethoxy-2-phenylacetophenone, 2-methoxy-2-phenylacetone,benzyl-dimethyl-ketal, ammonium persulfate, benzophenone, ethyl benzoinether, isopropyl benzoin ether, α-methyl benzoin ether, benzoin phenylether, 2,2-diethoxy acetophenone, 1,1-dichloro acetophenone,2,-hydroxy-2-methyl-1-phenylpropane-1-one, 1-hydroxy cyclohexyl phenylketone, anthraquinone, 2-ethyl anthraquinone, 2-chloro anthraquinone,thioxantone, isopropyl thioxantone, chloro thioxantone, 2,2-chlorobenzophenone, benzyl benzoate, bezoyl and the like. The initiator can begenerally used in an amount of 0.1–5.0% by weight of the entire polymerused for the UV-cured polymer layer.

The curing accelerator used for improving the curing speed in thepresent invention is an amine such as trimethylamine, tributylamine,triethanolamine, N-benzyldimethylamine and the like. The curingaccelerator can be generally used in an amount of 1.0–5.0% by weight ofthe entire polymer used for the UV-cured polymer layer.

Examples of the plasticizer which can be used in the present inventionmay include N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF),dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methylcarbonate (EMC), propylene carbonate (PC), acetonitrile and mixturesthereof, but not limited thereto. The amount of plasticizer used for thepolymer electrolyte can be preferably adjusted in the range of 100–2000%by weight to the entire polymer mixture.

Examples of the filler which can be used for the present invention mayinclude TiO₂, BaTiO₃, Li₂O, LiF, LiOH, Li₃N, BaO, Na₂O, MgO, Li₂CO₃,LiAlO₂, SiO₂, Al₂O₃, PTEE, an organic filler, a polymeric filler ormixtures thereof. The filler can improve porosity and mechanicalstrength of the electrolyte. The amount of the filler added ispreferably no more than 20% by weight of the entire polymer mixture.

Besides the above materials, the electrolyte of the present inventionmay include various types of additives such as an adhesive propertyenhancing material and a filler for improving the mechanical strengthand interfacial performance with the electrode.

A method for preparing the polymer electrolyte according to the presentinvention will now be described. After an oligomer having the formula 1,a function-II polymer and a function-III polymer are added to an organicelectrolyte solution and/or to an organic solvent, the resultant isdissolved or swelled by stirring at ambient temperature or in the rangeof 50–150° C. It is preferred that,the stirring is performed for atleast 3 hours in order to achieve mixing sufficiently. To the abovemixture, an initiator for UV curing and a curing accelerator are added,and then the solution is additionally stirred for from 30 seconds to 10minutes. After that, the resulting solution is cast onto a Mylar film orglass plate at a suitable thickness of no more than 100 μm, and then thecuring of the oligomer is performed by radiating UV rays alone orcombined with other methods. If it is necessary, an organic electrolytesolution may be further added to the obtained polymer electrolyte film.In order to exclude the effects of moisture, all of the above processesare preferably performed under the condition in which the humidity isbelow 10 ppm at ambient temperature. Curing with UV rays, heat orelectron beam highly depends on the intensity of energy sources, thecomposition of polymer mixture, the thickness of film and theatmospheric condition.

The UV-cured multi-component polymer blend electrolyte can be used forfabricating various types of lithium secondary batteries. Examplesinclude lithium secondary batteries with a mono-cell structure in whichan anode/a UV-cured multi-component polymer electrolyte/a cathode aresequentially stacked, or lithium secondary batteries with bi-cellstructure in which a cathode/a UV-cured multi-component polymerelectrolyte/an anode/a UV-cured multi-component polymer electrolyte/acathode are sequentially stacked. If it is necessary, a stackedstructure in which the above bi-cell structure are sequentially stackedagain may be used.

The anode and the cathode used for lithium secondary batteries are madeby mixing an appropriate amount of an active material, a conductivematerial, a binder and an organic solvent, followed by casting theobtained mixture onto both sides of copper and aluminum thin platerespectively, and then drying and rolling the resulting plate as in theconventional method. In more detail, the, anode is made of at least onematerial selected from the group consisting of graphite, cokes, hardcarbon, tin oxide, a lithiated material thereof, lithium and lithiumalloys. The cathode is made at least one material selected from thegroup consisting of LiCoO₂, LiNiO₂, LiNiCoO₂, LiMn₂O₄, V₂O₅ and V₆O₁₃.The organic electrolyte solution injected when batteries are fabricatedis a solution selected from the group consisting of solutions of alithium salt in EC-DMC, EC-DEC, EC-EMC, EC-PC and mixtures thereof, andsolutions in which any one of MA, MP, EA, EP, BC, γ-BL,DME, DMA and THFis added to the above lithium salt solutions, respectively. The copperand aluminum grids can be used in the form of a plate, a punched plate,an expanded plate, a porous plate or the like. If the organicelectrolyte solution is injected after stacking, a punched plate, anexpanded plate and a porous plate are more advantageous for efficientinjection of the solution.

The present invention will now be described in more detail by thefollowing Examples, to which the present invention is not limited.

EXAMPLES Example 1

A 5 wt % solution of a mixture (1:1 by weight) of polymethylmethacrylate(Polyscience, molecular weight 100,000) and P(VdF-HFP) (Atochem Kynar2801) which is in polyvinylidene fluoride group in DMC was prepared. 1 gof the obtained solution was added to 2 g of a liquid electrolytesolution which is a 1M LiPF₆ solution in a mixture (1:1 by weight) ofethylene carbonate/dimethyl carbonate containing 1 g of polyethyleneglycol diacrylate oligomer (Aldrich Co., molecular weight 742). Theresulting mixture was mixed enough to be homogeneous for at least 3hours and then cast onto a Mylar film at a thickness of 50 μm with adoctor blade method. UV rays were irradiated onto the obtained film witha UV lamp having a power of 100 W for about 1.5 hours to induce apolymerization of the oligomer, thereby to obtain a uniform UV-curedmulti-component polymer blend electrolyte. The obtained electrolyte wasclosely adhered onto both sides of a graphite anode and put togetherwith a lamination process. The obtained plate was cut so as to be 3 cm×4cm in size and then stacked it alternately with a LiCoO₂of 29 cm×3.9 cmin size. After terminals were welded onto the electrodes, the electrodeswere inserted into a vacuum casing. A 1M LiPF₆ solution in EC-EMC wasinjected into the casing, and then the casing was sealed, thereby toobtain a lithium secondary battery.

Example 2

A 5 wt % solution of a mixture (1:1 by weight) of polyacrylonitrile(Polyscience, molecular weight 150,000) and P(VdF-HFP) (Atochem Kynar2801) which is in polyvinylidene fluoride group in DMC was prepared. 1 gof the obtained solution was added to 2 g of a liquid electrolytesolution which is a 1M LiPF₆ solution in a mixture (1:1 by weight) ofethylene carbonate/dimethyl carbonate containing 1 g of polyethyleneglycol diacrylate oligomer (Aldrich Co., molecular weight 742). Theresulting mixture was mixed enough to be homogeneous for at least 3hours and then cast onto a Mylar film at a thickness of 50 μm with adoctor blade method. UV rays were irradiated onto the obtained film witha UV lamp having a power of 100 W for about 1.5 hours to induce apolymerization of the oligomer, thereby to obtain a uniform UV-curedmulti-component polymer blend electrolyte. The obtained electrolyte wasclosely adhered onto both sides of a graphite anode and put togetherwith a lamination process. The obtained plate was cut so as to be 3 cm×4cm in size and then stacked it alternately with a LiCoO₂ of 2.9 cm×3.9cm in size. After terminals were welded onto the electrodes, theelectrodes were inserted into a vacuum casing. A 1M LiPF₆ solution inEC-EMC was injected into the casing, and then the casing was sealed,thereby to obtain a lithium secondary battery.

Example 3

A 5 wt % solution of a mixture (1:1 by weight) of polymethylmethacrylate(Polyscience, molecular weight 100,000) and polyvinylchloride (Aldrich,molecular weight 150,000) in DMC was prepared. 1 g of the obtainedsolution was added to 2 g of a liquid electrolyte solution which is a 1MLiPF₆ solution in a mixture (1:1 by weight) of ethylenecarbonate/dimethyl carbonate containing 1 g of polyethylene glycoldiacrylate oligomer (Aldrich Co., molecular weight 742). The resultingmixture was mixed enough to be homogeneous for at least 3 hours and thencast onto a Mylar film at a thickness of 50 μm with a doctor blademethod. UV rays were irradiated onto the obtained film with a UV lamphaving a power of 100 W for about 1.5 hours to induce a polymerizationof the oligomer, thereby to obtain a uniform UV-cured multi-componentpolymer blend electrolyte. The obtained electrolyte was closely adheredonto both sides of a graphite anode and put together with a laminationprocess. The obtained plate was cut so as to be 3 cm×4 cm in size andthen stacked it alternately with a LiCoO₂ of 2.9 cm×3.9 cm in size.After terminals were welded onto the electrodes; the electrodes wereinserted into a vacuum casing. A 1M LiPF₆ solution in EC-EMC wasinjected into the casing, and then the casing was sealed, thereby toobtain a lithium secondary battery.

Example 4

A 5 wt % solution of a mixture (1:1 by weight) of polyacrylonitrile(Polyscience, molecular weight 150,000) and polyvinylchloride (Aldrich,molecular weight 150,000) in DMC was prepared. 1 g of the obtainedsolution was added to 2 g of a liquid electrolyte solution which is a 1MLiPF₆ solution in a mixture (1:1 by weight) of ethylenecarbonate/dimethyl carbonate containing 1 g of polyethylene glycoldiacrylate oligomer (Aldrich Co., molecular weight 742). The resultingmixture was mixed enough to be homogeneous for at least 3 hours and thencast onto a Mylar film at a thickness of 50 μm with a doctor blademethod. UV rays were irradiated onto the obtained film with a UV lamphaving a power of 100 W for about 1.5 hours to induce a polymerizationof the oligomer, thereby to obtain a uniform UV-cured multi-componentpolymer blend electrolyte. The obtained electrolyte was closely adheredonto both sides of a graphite anode and put together with a laminationprocess. The obtained plate was cut so as to be 3 cm×4 cm in size andthen stacked it alternately with a LiCoO₂ of 2.9 cm×3.9 cm in size.After terminals were welded onto the electrodes, the electrodes wereinserted into a vacuum casing. A 1M LiPF₆ solution in EC-EMC wasinjected into the casing, and then the casing was sealed, thereby toobtain a lithium secondary battery.

Example 5

A 5 wt % solution of a mixture (1:1 by weight) of polymethylmethacrylate(Polyscience, molecular weight 100,000) and P(VdF-HFP) (Atochem Kynar2801) which is in polyvinylidene fluoride group in EMC was prepared. 1 gof the obtained solution was added to 2 g of a liquid electrolytesolution which is a 1M LiPF₆ solution in a mixture (1:1 by weight) ofethylene carbonate/dimethyl carbonate containing 1 g of polyethyleneglycol diacrylate oligomer (Aldrich Co., molecular weight 742). Theresulting mixture was mixed enough to be homogeneous for at least 3hours and then cast onto a Mylar film at a thickness of 50 μm with adoctor blade method. UV rays were irradiated onto the obtained film witha UV lamp having a power of 100 W for about 1.5 hours to induce apolymerization of the oligomer, thereby to obtain a uniform UV-curedmulti-component polymer blend electrolyte. The obtained electrolyte wasclosely adhered onto both sides of a graphite anode and put togetherwith a lamination process. The obtained plate was cut so as to be 3 cm×4cm in size and then stacked it alternately with a LiCoO₂ of 2.9 cm×3.9cm in size. After terminals were welded onto the electrodes, theelectrodes were inserted into a vacuum casing. A 1M LiPF₆ solution inEC-EMC was injected into the casing, and then the casing was sealed,thereby to obtain a lithium secondary battery.

Example 6

A 5 wt % solution of a mixture (1:1 by weight) of polymethylmethacrylate(Polyscience, molecular weight 100,000) and P(VdF-HFP) (Atochem Kynar2801) which is in polyvinylidene fluoride group in DMC was prepared. 1 gof the obtained solution was added to 2 g of a liquid electrolytesolution which is a 1M LiPF₆ solution in a mixture (1:1 by weight) ofethylene carbonate/dimethyl carbonate containing 1 g of polyethyleneglycol diacrylate oligomer (Aldrich Co., molecular weight 742). Theresulting mixture was mixed enough to be homogeneous for at least 3hours and then cast onto a Mylar film at a thickness of 50 μm with adoctor blade method. UV rays were irradiated onto the obtained film witha UV lamp having a power of 100 W for about 1.5 hours to induce apolymerization of the oligomer, thereby to obtain a uniform UV-curedmulti-component polymer blend electrolyte. The obtained electrolyte wasclosely adhered onto both sides of a graphite anode and put togetherwith a lamination process. The obtained plate was cut so as to be 3 cm×4cm in size and then stacked it alternately with a LiCoO₂ of 2.9 cm×3.9cm in size. After terminals were welded onto the electrodes, theelectrodes were inserted into a vacuum casing. A 1M LiPF₆ solution inEC-EMC was injected into the casing, and then the casing was sealed,thereby to obtain a lithium secondary battery.

Example 7

A 5 wt % solution of a mixture (1:1 by weight): of polyacrylonitrile(Polyscience, molecular weight 150,000) and P(VdF-HFP) (Atochem Kynar2801) which is in polyvinylidene fluoride group in DMC was prepared. 1 gof the obtained solution was added to 2 g of a liquid electrolytesolution which is a 1M LiPF₆ solution in a mixture (1:1 by weight) ofethylene carbonate/dimethyl carbonate containing 1 g of polyethyleneglycol diacrylate oligomer (Aldrich Co., molecular weight 742). Theresulting mixture was mixed enough to be homogeneous for at least 3hours and then cast onto a Mylar film at a thickness of 50 μm with adoctor blade method. UV rays were irradiated onto the obtained film witha UV lamp having a power of 100 W for about 1.5 hours to induce apolymerization of the oligomer, thereby to obtain a uniform UV-curedmulti-component polymer blend electrolyte. The obtained electrolyte wasclosely adhered onto both sides of a graphite anode and put togetherwith a lamination process. The obtained plate was cut so as to be 3 cm×4cm in size and then stacked it alternately with a LiCoO₂ of 2.9 cm×3.9cm in size. After terminals were welded onto the electrodes, theelectrodes were inserted into a vacuum casing. A 1M LiPF₆ solution inEC-EMC was injected into the casing, and then the casing was sealed,thereby to obtain a lithium secondary battery.

Example 8

A 5 wt % solution of a mixture (1:1:1 by weight) ofpolymethylmethacrylate (Polyscience, molecular weight 100,000),P(VdF-HFP) (Atochem Kynar 2801) which is in polyvinylidene fluoridegroup and polyacrylonitrile (Polyscience, molecular weight 150,000) inDMC was prepared. 1 g of the obtained solution was added to 2 g of aliquid electrolyte solution which is a 1M LiPF₆ solution in a mixture(1:1 by weight) of ethylene carbonate/dimethyl carbon containing 1 g ofpolyethylene glycol diacrylate oligomer (Aldrich Co., molecular weight742). The resulting mixture was mixed enough to be homogeneous for atleast 3 hours and then cast onto a Mylar film at a thickness of 50 μmwith a doctor blade method. UV rays were irradiated onto the obtainedfilm with a UV lamp having a power of 100 W for about 1.5 hours toinduce a polymerization of the oligomer, thereby to obtain a uniformUV-cured multi-component polymer blend electrolyte. The obtainedelectrolyte was closely adhered onto both sides of a graphite anode andput together with a lamination process. The obtained plate was cut so asto be 3 cm×4 cm in size and then stacked it alternately with a LiCoO₂ of2.9 cm×3.9 cm in size. After terminals were welded onto the electrodes,the electrodes were inserted into a vacuum casing. A 1M LiPF₆ solutionin EC-EMC was injected into the casing, and then the casing was sealed,thereby to obtain a lithium secondary battery.

Example 9

A 5 wt % solution of a mixture. (1:1:1:1 by weight) ofpolymethylmethacrylate (Polyscience, molecular weight 100,000),P(VdF-HFP) (Atochem Kynar 2801) which is in polyvinylidene fluoridegroup, polyacrylonitrile (Polyscience, molecular weight 150,000) andpolyvinylchloride (Aldrich, molecular weight 150,000) in DMC wasprepared. 1 g of the obtained solution was added to 2 g of a liquidelectrolyte solution which is a 1M LiPF₆ solution in a mixture (1:1 byweight) of ethylene carbonate/dimethyl carbonate containing 1 g ofpolyethylene glycol diacrylate oligomer (Aldrich Co., molecular weight742). The resulting mixture was mixed enough to be homogeneous for atleast 3 hours and then cast onto a Mylar film at a thickness of 50 μmwith a doctor blade method. UV rays were irradiated onto the obtainedfilm with a UV lamp having a power of 100 W for about 1.5 hours toinduce a polymerization of the oligomer, thereby to obtain a uniformUV-cured multi-component polymer blend electrolyte. The obtainedelectrolyte was closely adhered onto both sides of a graphite anode andput together with a lamination process. The obtained plate was cut so asto be 3 cm×4 cm in size and then stacked it alternately with a LiCoO₂of2.9 cm×3.9 cm in size. After terminals were welded onto the electrodes,the electrodes were inserted into a vacuum casing. A 1M LiPF₆ solutionin EC-EMC was injected into the casing, and then the casing was sealed,thereby to obtain a lithium secondary battery.

Comparative Example 1

2 g of polyethyleneglycoldiacrylate oligomer (Aldrich, molecular weight742) was added to 2 g of a liquid electrolyte solution of a 1M LiPF₆solution in a mixture (1:1 by weight) of ethylene carbonate/ethyl methylcarbonate. The resulting mixture was mixed enough and then cast onto aglass plate. UV rays were irradiated onto the obtained plate with a UVlamp having a power of 100 W for about 1.5 hours to induce apolymerization of the oligomer, thereby to obtain a UV-cured polymerelectrolyte. The obtained electrolyte was closely adhered onto bothsides of a graphite anode and put together with a lamination process.The obtained plate was cut so as to be 3 cm×4 cm in size and thenstacked it alternately with a LiCoO₂ of 2.9 cm×3.9 cm in size. Afterterminals were welded onto the electrodes, the electrodes were insertedinto a vacuum casing. A 1M LiPF₆ solution in EC-EMC was injected intothe casing, and then the casing was sealed, thereby to obtain a lithiumsecondary battery.

Comparative Example 2

2 g of polyvinylidenefluoride (PVdF, Kynar 761) was added to 14 g of aliquid electrolyte solution of a 1M LiPF₆solution in a mixture (1:1 byweight) of ethylene carbonate/ethyl methyl carbonate. The resultingmixture was mixed for 3 hours at 150° C. and then cast onto a Mylar filmat a thickness of 50 μm with a doctor blade method, to obtain a polymerelectrolyte. The obtained electrolyte was closely adhered onto bothsides of a graphite anode and put together with a lamination process.The obtained plate was cut so as to be 3 cm×4 cm in size and thenstacked it alternately with a LiCoO₂ of 2.9 cm×3.9 cm in size. Afterterminals were welded onto the electrodes, the electrodes were insertedinto a vacuum casing. A 1M LiPF₆ solution in EC-EMC was injected intothe casing, and then the casing was sealed, thereby to obtain a lithiumsecondary battery.

Test Results

Example 10

Ionic conductivities of the UV-cured multi-component polymer blendsobtained in Examples 1–4 and of the polymer electrolyte obtained inComparative Example 1 were measured, and the results are shown inFIG. 1. As shown in FIG. 1, the ionic conductivities of the UV-curedmulti-component polymer blend according to the present invention are10⁻³ S/cm or more at ambient temperature and superior to that of theconventional UV-cured polymer electrolyte. Furthermore, a stretchingratio of the polymer blend electrolyte of the present invention was50%–90% higher than that of the electrolyte of Comparative Example 1,and accordingly, its mechanical property was also improved.

Example 11

Charge/discharge tests were performed by charging the batteries obtainedin Examples 1–9 and Comparative Examples 1–2 with C/2 constant currentand 4.2V constant voltage, and followed by discharging them with C/2constant current, in order to examine electrode capacities based oncathodes and a cycle life. The results are shown in FIG. 2.

As shown in FIG. 2, the lithium secondary batteries according toExamples 1–9 comprising the polymer blend electrolyte of the presentinvention are superior to those of the lithium secondary batteriesaccording to Comparative Examples 1 and 2. In addition, the lithiumsecondary batteries of the present invention are superior in cyclecharacteristics in which their capacities are not reduced regardless ofrepeated charging/discharging. Therefore, it was found that the polymerblend electrolyte according to the present invention improves theelectrode capacity and cycle life of batteries. Such improvement seemsto be resulted from the reduction of interfacial resistance due to astrong adhesive force between the electrode and the polymer blendelectrolyte, and superior ionic conductivity of the polymer blendelectrolyte.

Example 12

Low- and high-temperature characteristics of the lithium secondarybatteries obtained in Example 1 and Comparative Example 1 were testedwith a charging/discharging method in which the batteries were chargedwith C/2 constant current and 4.2V constant voltage, and then dischargedwith C/5 constant current. The results are shown in FIGS. 3 a and 3 b.As shown in FIGS. 3 a and 3 b, low- and high-temperature characteristicsof the lithium secondary battery comprising the polymer blendelectrolyte according to the present invention has been improved morethan that of the battery comprising the conventional polymerelectrolyte.

Example 13

High-rate discharge characteristics of the lithium secondary batteriesobtained in Example 1 and Comparative Example 1 were tested with acharging/discharging method in which the battery was charged with C/2constant current and 4.2V constant voltage, and then discharged whilechanging the constant current into C/5, C/2, 1 C, and 2 C. The resultsare shown in FIGS. 4 a and 4 b. As shown in FIGS. 4 a and 4 b, thelithium secondary battery comprising the polymer blend electrolyteaccording to the present invention exhibited 95% and 90% of capacities,respectively, when discharged with 1 C and 2 C for 0.2 C discharging.However, the battery of the Comparative Example 1 exhibited lowperformances of 87% and 56%, respectively. Therefore, it was found thathigh-rate discharge characteristics of the lithium secondary batterycomprising the polymer blend electrolyte according to the presentinvention is superior to those of the conventional battery.

INDUSTRIAL APPLICABILITY

As so far described, the polymer blend electrolyte according to thepresent invention is superior in adhesive property and mechanicalstability. According to the present invention, it is possible to providea lithium secondary battery which is superior in low- andhigh-temperature characteristics, high-rate discharge characteristics,capacity, cycle life and stability. Accordingly, the present inventioncan be applied to various types of small electronic appliances,communication devices and as a power source for an electric car.

1. A UV-cured multi-component polymer blend electrolyte comprising: A) afunction-I polymer obtained by curing anethyleneglycoldi-(metha)acrylate oligomer having the following formula 1by UV irradiation,CH₂═CR¹COO(CH₂CH₂O)_(n)COCR²═CH₂  (1) wherein, R¹ and R² areindependently a hydrogen or methyl, and n is an integer of 3–20; B) afunction-II polymer selected from the group consisting ofpolyacrylonitrile (PAN), polymethylmethacrylate (PMMA) and mixturesthereof; C) a function-III polymer selected from the group consisting ofpolyvinylidene fluoride (PVdF), polyvinyl chloride (PVC) and mixturesthereof; and D) an organic electrolyte solution in which a lithium saltis dissolved in an organic solvent.
 2. The electrolyte according toclaim 1, wherein the polymer of PAN group is selected from the groupconsisting of polyacrylonitrile, and poly(acrylonitrile-methylacrylate),the polymer of PMMA group is selected from the group consisting ofpoly(methyl methacrylate), poly(methyl methacrylate-co-ethyl acrylate),poly(methyl methacrylate-co-methacrylic acid), the PVdF group isselected from the group consisting of polyvinylidene difluoride,poly(vinylidenedifluoride-hexafluoroprophylene), and the polymer of PVCgroup is selected from the group consisting of polyvinylchloride,poly(vinylchloride-co-acrylonitrile).
 3. The electrolyte according toclaim 1, wherein the lithium salt is selected from the group consistingof LiPF₆, LiClO₄, LiAsF₆, LiBF₄, LiCF₃SO₃, Li(CF₃SO₂)₂N and combinationsthereof.
 4. The electrolyte according to claim 1, wherein the organicsolvent is ethylene carbonate, propylene carbonate, diethyl carbonate,dimethyl carbonate, ethyl methyl carbonate or mixtures thereof.
 5. Theelectrolyte according to claim 4, wherein the organic solvent furthercomprises a solvent which is selected from the group consisting ofmethyl acetate, methyl propionate, ethyl acetate, ethyl propionate,butylene carbonate, γ-butyrolactone, 1,2-dimetoxyethane,dimethylacetamide, tetrahydrofuran and mixtures thereof.
 6. Theelectrolyte according to claim 1, further comprises at least onecomponent selected from the group consisting of a plasticizer, a porousfiller, an initiator for UV curing and a curing accelerator.
 7. Theelectrolyte according to claim 6, wherein the plasticizer is selectedfrom the group consisting of N,N-dimethylacetamide,N,N-dimethylformamide, dimethyl carbonate, ethylene carbonate, ethylmethyl carbonate, propylene carbonate, acetonitrile and mixturesthereof.
 8. The electrolyte according to claim 6, wherein the porousfiller is selected from the group consisting of TiO₂, BaTiO₃, Li₂O, LiF,LiOH, Li₃N, BaO, Na₂O, MgO, Li₂CO₃, LiAlO₂, SiO₂, Al₂O₃, PTEE, anorganic filler, a polymeric filler and mixtures thereof.
 9. Theelectrolyte according to claim 6, wherein the initiator for UV-curing isselected from the group consisting of2,2-dimethoxy-2-phenylacetophenone, 2-methoxy-2-phenylacetone,benzyl-dimethyl-ketal, ammonium persulfate, benzophenone, ethyl benzoinether, isopropyl benzoin ether, a-methyl benzoin ether, benzoin phenylether, 2,2-diethoxy acetophenone, 1,1-dichloroacetophenone,2-hydroxy-2-methyl-1-phenyipropane-1-one, 1-hydroxycyclohexyl phenylketone, anthraquinone, 2-ethylanthraquinone, 2-chloroanthraquinone,thioxantone, isopropyl thioxantone, chlorothioxantone,2,2-chlorobenzophenone, benzyl benzoate, bezoyl benzoate and mixturesthereof.
 10. The elect rolyte according to claim 6, the curingaccelerator is an amine compound.
 11. The elect rolyte according toclaim 10, wherein the amine compound is selected from the groupconsisting of trimethylamine, tributylamine, triethanolamine andN-benzyldimethylamine.
 12. A lithium secondary battery comprising acathode, an anode and the electrolyte according to claim
 1. 13. Thebattery according to claim 12, wherein the cathode comprises at leastone cathode active material selected from the group consisting ofLiCoO₂, LiNiO₂, LiNiCoO₂, LiMn₂O₄, V₂O₅ and V₆O₁₃.
 14. The batteryaccording to claim 12, wherein the anode comprises at least one anodeactive material selected from the group consisting of graphite, cokes,hard carbon, tin oxide, lithiated materials thereof, lithium and lithiumalloys.
 15. The battery according to claim 12, which is in a mono-cellstructure.
 16. The battery according to claim 12, which is in a bi-cellstructure.